perf tools: Generalize perf_header__adds_read()

Renaming it to perf_header__process_sections() and passing a
callback to handle each feature.

The next changesets will introduce 'perf buildid-list' that will
handle just the HEADER_BUILD_ID table, ignoring all the other
features.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <1258396365-29217-3-git-send-email-acme@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>